We are focussing on three aspects of cell interactions in the myxobacteria: (1) Regulated cell death plays a widespread and important role in the development of higher organisms. It has hitherto not been shown in bacteria. We propose that cell death of a portion of the myxobacterial population is a requisite of normal and complete development. We plan to investigate the role, mechanism, and regulation of this phenomenon. (2) Cell-surface interactions have been implicated in a wide variety of activities of higher cells. They also appear to play a role in cell interactions among myxobacteria. We intend to use concanavalin A as a probe to investigate changing patterns of surface polysaccharides during development and also to isolate conA binding sites involved in these interactions. We also will examine the role and nature of surface glycosyl transferase during development. (3) The myxobacterial population differentiates into four clearly distinct cell types whch interact developmentally with each other and separately have differing developmental potentials. We are examining this phenomenon in terms of the nature of the differences, the basis of the conversion, the interplay among the types and the differential developmental roles.